1. Field of the Invention
This invention relates to the field of frictional transmission chains, and in particular, to frictional transmission chains of an entraining type power transmitting apparatus, for use in infinitely variable speed shift mechanisms and the like.
2. Prior Art
Until recently, it has been known to use a rubber V belt as an entrained transmission belt in an entraining drive type infinitely variable speed shift mechanisms. Recently, a metal V belt has been developed which has attracted much attention. A number of frictional transmission V blocks are lined up contiguously to each other and an endless steel-made band is passed through a hollow space defined in those blocks. Reference may be made to Japanese Patent Laid-Open Specification No. 54-52253.
Japanese Patent Laid-Open Specification No. 59-17043 discloses an improved metal V belt which has overcome a serious drawback of the steel-made band employed in such metal V belt. The steel band is subject to metal fatigue when it is flexed because it undergoes a tensile force on the outer side and a compression force on the inner side. More specifically, the improved metal V belt employs a link chain in place of a steel-made band. However, both the link chain and the steel band are slidable relative to frictional transmission V blocks through wihch the line chain or band is passed. Accordingly, both the steel band and the link chain are assembled to be slidable relative to the frictional transmission V blocks.
Furthermore, in both the steel band and chain link chains, each friction contact surface of each V block is in the form of a single plane which therefore makes only a single line or single point contact against the conical contact surface serving as a frictional transmission surface of a drive pulley. As a result, the friction contact area between the V block and the drive pulley is very small.
In such construction as described above, slippage occurs between the V block and the steel band or link chain upon flexing while turning round a pulley. The slippage in turn wears away the V blocks and the steel band or link chain, significantly reducing the durability of metal V belts.
The underlying theory of both constructions described above is transmitting power due to a thrust imposed from one V block to the subsequent V block, and therefore, in neither assembly is the steel-made band or link chain directly relied upon to contribute to power transmission. In each case, the steel-made band or chain link functions merely to hold a number of aligned V blocks in the form of an endless belt. Relative slippage between the V block and the steel or link chain was unavoidable. Further, a V groove of the V-groove pulley causes a tight holding pressure to be exerted on the V block, so that the steel-made band and link chain are subjected to a tensile force to balance with that pressure. This results in breakage due to metal fatigue, as well as wear of such band and chain.
Moreover, because of the small contact area between the friction contact surface of the V block and the conical contact surface of the V-groove pulley as previously noted, the large, tight holding pressure exerted from the V-shaped inclined surface of the V-groove pulley on the V block is concentrated on that small contact area, thereby making damage to the V block more likely. At the same time, the small contact area also necessarily reduces the efficiency of such friction transmission.
This invention disregards the underlying theoretical basis of known link chain friction drive chains, wherein power due to a thrust imposed on one V block is transmitted to a subsequent V block, and so on. Instead, this invention makes use of a link chain as a pulling transmission medium, even though it has been accepted by those skilled in the art that pulling kinds of power transmission due to a chain must always be effected in the form of an engagement transmission (e.g. toothed wheel and link chain). An endless transmission chain is passed through a central hollow space defined in a number of frictional transmission V blocks which are aligned contiguously to each other. The V blocks are each mounted over a link plate connection pin of the chain, and frictional transmission contact surfaces, symmetrical transversely, project from both generally V-shaped inclined surfaces (front and rear) of the V block. A infinitely variable speed shift mechanism has a pair of frictional transmission V-groove pulleys with the opposite surfaces formed into a V-shape and a variable spacing therebetween. Therefore, when an endless frictional transmission chain according to this invention is stretched between the pair of pulleys disposed in spaced relation, the friction contact surfaces projecting from both outer inclined surfaces of the frictional transmission V block are brought into contact with the opposite surfaces of the conical V-groove of the pulley at plural locations on each side. The V blocks are tightly held therebetween because the projected friction contact surfaces are formed to be transversely symmetrical along the radial direction of the pulley. As a result, the chain is driven while being pulled via the connection pins of the chain due to frictional transmission between the pulley and the V block. The V blocks transmit power only between the pulleys and the link-pin chain. Power is transmitted between the pulleys only by the link-pin chain, and not by forces transmitted between contiguous or adjacent V blocks.
Many other problems have been associated with friction drive chains, particularly those with link chains.
Conventional friction drive chains comprise a multiplicity of link plates press fitted about bushings and connected by pins to form an endless chain. The chain is disposed in a central cavity defined by openings in a plurality of pairs of generally channel-shaped struts, which from the individual V-blocks. The pairs of struts may be held together, for example, by pins, welding or adhesive. The same number of inner and outer link plates are usually employed. Alternatively, the number of the outer link plates has been equal to the number of the inner link plates plus one so that a symmetric arrangement may be achieved with respect to the longitudinal centerline of the chain, as shown in Japanese Laid-Open Patent Specification No. 226729/1984.
In either event, however, all of the link plates are equal in thickness, even though the outermost link plates which are subjected to the largest load begin to fracture first, and this fracture defines the end of the operational life of the chain. A continuously variable transmission (CVT) chain bears the force transmitted from the sheaves (of the pulleys) to the struts on both sides thereof, as opposed to a roller chain. Therefore, it is on the outermost link plates that the largest force acts.
If the chain is used for a speed change system in which only the sheaves on one side are driven (to vary speed), its centerline is displaced and the chain receives not only a static tensile load, but also a repeated bending load. The largest repeated bending stress occurs in the outermost link plates, and the outermost link plates are, therefore, the first to break.
According to this invention, this problem is overcome by providing outermost link plates having a thickness which is greater than that of the other link plates. Alternatively, the greater thickness can be achieved by using a greater number of link plates of identical thickness. Accordingly, the outermost link plates have a relatively larger cross sectional area (singly or in composite) and can, therefore, withstand a larger load.
In conventional friction drive chains, the opposite ends of each connecting pin are press fitted in the pair of struts, respectively. In friction drive chains of the type in which the connecting pins so extend into the struts and support them, the frictional force produced between the struts and the pulley sheaves is entirely transmitted to the connecting pins. The force acting on the connecting pins is considerably large, and the connecting pins are, therefore, press fitted in the struts so that there may not exist therebetween any clearance causing the uneven wear thereof. The press fitting of the connecting pins also has the advantage of facilitating the alignment of each pair of struts.
Insofar as each connecting pin is immovably fitted in the struts at the opposite ends thereof, however, the areas of its contact with the bushings of the link plates always remain unchanged. The connecting pins are therefore worn only on the opposite sides thereof as viewed longitudinally along the chain. This wear results in the elongation or loosening of the chain.
According to this invention, the connecting pins are not press fitted in the struts. Instead, the problem of uneven wear is solved by the provision of a bushing which is press fitted in each strut, and in which one of the connecting pins is rotatably received. Therefore, as each pin rotates randomly in the busings the entire periphery of each conecting pin defines a contact surface with the link bushings. Accordingly, the pins wear evenly.
It is difficult to fit a single link plate accurately about a bushing and it is, therefore, usual to fit two link plates together. The surfaces of the line plates are flush with the end surfaces of the bushing. This arrangement prevents the satisfactory flow of a lubricant into the gaps between adjoining bushings.
According to this invention, the problem of insufficient lubrication is solved by providing bushing each having a portion projecting laterally from each side of the link plates in which it is fitted. The link plates fitted about every two adjoining bushings in an assembled chain therefore have a gap or clearance which enables a lubricant to flow through the gaps between the bushings into the space between the bushings and a connecting pin.
It is possible to modify the cross sectional shape of each strut to ensure the satisfactory application of a lubricant to the chain, even when it is moving. The upper and lower ends of the struts may have a substantially trapezoidal cross section and be suitable for the application of a lubricant by nozzles arranged by perpendicularly to the chain. Alternatively, the upper and lower ends of the struts may have a substantially rhomboidal cross section and be suitable for the application of a lubricant by nozzles arranged at an inclined angle relative to the chain. The effective supply of a lubricant into the clearances between the bushings and the connecting pins renders the chain highly resistant to wear and thereby prolongs its life.
It is a characteristic of a CVT having a friction drive chain that, if the shafts for the sheaves has a fixed distance therebetween and the friction chain has a fixed length, the winding pitch diameters of the sheaves vary differently with a change of speed. In a speed change mechanism in which the sheave on one side is fixed and the sheave on the other side is movable, the centerline of the chain is therefore displaced with each change of speed.
In conventional friction drive chains for a CVT, the centerline of the V blocks or struts (friction blocks) is aligned with the line generating the radius of the sheaves when the struts are brought into winding contact with the sheaves. The struts and the pins are fixed to one another and all of the link plates are loosely fitted, that is, laterally slidable on the pins, relative to one another. Inasmuch as all of the link plates are loosely fitted on the connecting pins 4 (sometimes no bushing is employed), the transverse displacement of the chain (or the displacement of its centerline) is limited to an amount defined by the sum of gaps or clearances which is not great enough even for lubrication, as noted above.
According to this invention, the problems associated with displacement of the centerline of the chain are solved by firstly, using a bushing press fitted in each of the struts, ends of each of the pins being rotatably received in the bushings, and secondly, the pins carrying a plurality of fixed link plates and a plurality of laterally movable link plates. The centerline of a chain according to this construction is capable of displacement for every two pitches (the pitch being deemed the longitudinal width of the V blocks or struts). The displacement between the shafts amounts to a range which is equal to one half of the pitch number therebetween, multiplied by the transverse clearance for each pitch.
A problem which often arises with friction drive trains, particularly when the chain is used in an automobile, is the noise which is produced by the engagement of the V blocks (or struts) and pulley sheaves. The noise, reaching its peak at a regular or resonant frequency, is often intolerably unpleasant to persons in the automobile or otherwise close by. Insofar as the chain is moved by the engagement of the regularly repeated contact surfaces of the same shape with the sheaves, a loud noise is produced having a basic frequency which is determined by the number of the V blocks contacting the sheaves during each second.
According to this invention, the noise problem is solved by a friction drive chain having a plurality of V-shaped contact surfaces projecting from each side thereof and spaced apart from one another by an irregular distance. Alternatively, the position of the contact surfaces on each block can be varied.
As the intervals of contact between the sheaves and the V blocks are necessarily irregular, their contacts are substantially free from any basic frequency. It is possible to lower the peak of the basic frequency in the frequency spectrum of the noise produced by their contact. Therefore, it is possible to reduce the noise. If the intervals of contact between the sheaves and the V blocks are periodically varied, it is possible to control the basic frequency in the frequency spectrum of the noise produced by their contact and thereby convert the noise to something that is not so unpleasant.
The chains utilized in the art generally comprise a plurality of inner links formed by inner link plates press fitted about bushings, and a plurality of outer links formed by outer link plates press fitted about pins and connected to the inner links in an alternate fashion as noted. If a tensile load bears on the chain, bending and shearing stresses act on the pins and the bushings, and tensile stresses act on the link plates. The areas surrounding the holes of the link plates in which the pins and the bushings are fitted eventually yield to the tensile stress and undergo plastic deformation. This deformation gives rise to a reduction in the force holding the outer link plates and the pins together, and the inner link plates and the bushings together, thereby loosening the outer link plates relative to the pins, or the inner link plates relative to the bushings, or both. This reduction in force and the loosening lower the durability of the chain and can cause accidents or problems, such as the fracture of the link plates, pins and bushings due to fatigue or wear.
A solution to this problem is proposed in Japanese Patent Publication No. 15926/1975. It discloses the welding of the link plates to the pins or bushings. The welding proposed, however, is carried out along the entire periphery of the pins or bushings. The heat applied for welding extends even to the friction surfaces of the pins or bushings and is very likely to adversely affect the heat treatment which has been given to those surfaces to improve their wear resistance.
According to this invention, the problem of reduction in heat resistance is solved by welding each link plate to a pin or bushing only along a semicircular joint located toward the center of the link plate. The joint need not necessarily be continuous, or even extend fully over 180.degree. around the pin or bushing.
The partial welding along the semicircular joint minimizes the effect of heat on the other or unwelded area and prevents the development of any gap which might occur between the link plate and the bushing or pin when the chain is loaded. Thus, this invention reduces the concentration of stress on the welded joint and improves the fatigue resistance and strength of the chain.
Each of the problems noted herein is more or less serious depending upon the working environment. Accordingly, the application of one, of several or of all the proposed solutions will be more or less appropriate under different circumstances.